1. Field of the Invention
The present invention relates, generally, to thermo-forming machines, and more specifically, to adjustable clamp frames used to secure work pieces, such as plastic sheets of varying sizes, as the work pieces are cycled between stages within the machine wherein they are alternately heated and then formed to a particular shape defined by a mold.
2. Description of the Related Art
Thermo-forming machines are used in the manufacture of contoured plastic articles and the like. Machines of this type typically include a source of heat, such as an infrared or convection oven, and a mold. Thus, the ovens may be either gas fired or electric. A plastic, sheet-like work piece is cycled between the oven, where it is heated until it has become plasticized, and the mold where the work piece is formed into a desired shape. The mold may include at least one die and a pre-draw box, pressure plate or match tooling. The mold may thus be vacuum actuated, use air assisted pressure or simple mechanical force, as with match tooling, to form the plastic part. In the case of vacuum actuated molds, the die usually has a perforated surface. A vacuum is applied to this surface through the perforations which draws the heated sheet into contact with the surface of the die thereby imparting the shape of the die to the work piece. The newly formed plastic article is allowed to cool and is removed from the machine. The process is then repeated.
A clamp frame is typically used to secure the sheet-like workpiece in the machine, advance the work piece into the oven until it has become sufficiently plasticized and then to position the heated work piece adjacent the perforated die for molding. Clamp frames typically include a pair of opposed longitudinal frame members as well as a pair of opposed transverse frame members. Each frame member may include one or more clamps used to fix the workpiece relative to the machine.
In the past, it was known to use different sized clamp frames to accommodate workpieces of varying sizes. In this case, the clamp frames had to be changed when the dimension of the plastic sheet to be formed varied by more than one half inch. This was usually done immediately after a job run had been completed and usually while the frames were still relatively hot. It was found that this required considerable, undesirable work and time to remove the hot frame and install a new one for the next job. More specifically, this effort required disconnecting air lines, removing transverse frame members and loosening longitudinal frame members. The longitudinal frame members were then moved toward or away from each other to accommodate the size of the new plastic sheet workpiece. Transverse frame members which matched the size of the new workpiece were then installed on the frame, all fasteners were tightened and air lines reconnected. The operator was thus required to maintain a number of transverse frame members on hand to accommodate the varying dimensions of the workpiece formed by the thermo-forming machine. Obviously, this process was not consistent with modern manufacturing principles that require quick tool changes, reduced downtime for the machine and profitable short runs which minimize material and finished product inventories.
Accordingly, it became known in the art to employ transverse frame members which were large enough to accommodate movement of the longitudinal frame members outwardly to the maximum distance allowed by a particular clamp frame and which were also adjustable in finite, predetermined increments toward and away from one another. While this was an improvement over earlier practices, problems still remained. Any given clamp frame was still limited by the incremental adjustable distance of the transverse frame member toward and away from one another such that only specific changes in the dimensions of the workpiece could be accommodated. In addition, the relative movement of the transverse and longitudinally extending frame members sometimes caused interference between clamps on adjacent frame members.
Thereafter, clamp frames having opposed longitudinal and transverse frame members which were infinitely adjustable relative to one another became known in the art thereby solving the problem associated with incrementally adjustable frame members mentioned above. However, the devices proposed in the related art are rather mechanically complex or otherwise not cost-effective and thus have not been commercially adopted to any significant extent. Furthermore, the problems associated with confronting clamps on adjacent frame members still remain.
In response to this persistent problem, it became known in the art to position the clamps on the longitudinal and transverse frame members so that they were offset, above or below, an adjacent clamp. Unfortunately, this has not always eliminated interference between clamps during adjustment and also resulted in that the edges of the workpiece were clamped on different planes causing unacceptable distortion of the workpiece prior to and even after forming the plastic article.
Thus, there remains a need in the art for a clamp frame having transverse and longitudinal frame members which are adjustable toward and away from one another along a continuum and wherein the clamps employed with the frame members fix the edges of the workpiece on a common plane. In addition, there is a need in the art for such a clamp frame wherein the clamps located on adjacent transverse and longitudinal frame members do not confront one another or otherwise interfere with each other while the frame members are being adjusted. Still further, there is a need in the art for such a clamp frame which is easy to manufacture, simple to operate and which may be competitively priced.
The present invention overcomes the deficiencies of the related art in an adjustable clamp frame for securing a workpiece in a thermo-forming machine. The clamp frame of the present invention includes a pair of opposed, transverse cross members, each of which are adjustable along a continuum toward and away from one another. Each transverse cross member includes at least one clamping member for securing a work piece to the frame by clamping the respective edges thereof. The clamp frame also includes a pair of opposed, longitudinal cross members, each of which are adjustable along a continuum toward and away from one another. Each longitudinal cross member includes at least one clamping member for securing a work piece to the frame by clamping the respective edges thereof. The clamping members for each of the respective pair of opposed transverse and longitudinal cross members are adapted to be disposed on a common plane when the workpiece is secured in the frame. At least one of the pair of transverse and longitudinal cross members are movable such that the associated clamping members of the respective cross members are spaced from the common plane allowing for movement of the transverse and longitudinal cross members toward and away from one another along a full continuum defined by the clamp frame when the position of the cross members is adjusted.
One advantage of the present invention is that it provides a clamp frame for securing a workpiece in a thermo-forming machine with the clamp frame having opposed transverse and longitudinal frame members which are adjustable toward and away from one another along a continuum. Another advantage of the present invention is that the clamps employed on the opposed transverse and longitudinal frame members are adapted to be disposed on a common plane such that there is no distortion of the edges of the workpiece during the forming process.
Still another advantage of the present invention is that at least one of the pair of transverse and longitudinal frame members are movable such that their associated clamps are spaced from the common plane allowing or relative movement of the transverse and longitudinal frame members toward and away from one another along a full continuum defined by the clamp frame without interference or confronting contact between the clamps.
Other objects, features and advantages of the present invention will be readily appreciated as the same becomes better understood after reading the subsequent description taken in connection with the accompanying drawings.